During the Norwegian Antarctic Research Expedition 1993/94, field studies were conducted on a blue-ice field in Jutulgryta, Dronning Maud Land. Measurements of sub-surface temperatures revealed that temperatures in blue ice were about 6°C higher than in the adjacent snow. Despite the predominantly negative air temperatures, a sub-surface melt layer was discovered within the uppermost metre of the blue ice. Here the temperature maximum was consistent throughout the entire month of observations, and resulted in both internal melt and water transport. The melting is a consequence of solar radiative penetration and absorption within the ice, i.e. the “solid-state greenhouse”. Sensitivity experiments using a non-stationary combined radiative and thermodynamic model reveal that the physical properties (here extinction coefficient, radiation transmittance and albedo) strongly control the formation and vertical extent of the melt layer. The persistence of the sub-surface melt layer increases the runoff volume from blue-ice fields, which otherwise might be restricted to a few yearly events when air temperatures reach or exceed the freezing point. The conditions required for melting activity are marginal in Jutulgryta. Hence, this phenomenon may serve as an indicator of climate fluctuations in the area.

An Antarctic Circumpolar Wave (ACW) is simulated by a global coupled ocean-atmosphere model. Time-longitude diagrams of anomalies in sea-surface temperature (SST) and sea-surface salinity (SSS) show that anomalies propágale eastward, taking 20-30 years to encircle the pole. The time taken is 2-3 times longer than indicated by observations, due to the relatively slow speed of the modelled Antarctic Circumpolar Current (ACC). High-SSS anomalies correspond to high-SST anomalies and high-density anomalies, and thus to low sea-surface height anomalies, indicating that salinity IS a dominant factor for dynamics with in the Southern Ocean and is indispensable for understanding the mechanism of the ACW. Sea-ice formation is suppressed southward of warm, saline surface-water regions. High sea-ice concentration anomalies correspond to thick sea-ice anomalies. Empirical orthogonal function analyses of SSTanomalies for both model and observation show that the dominant mode in the Southern Ocean has a spatial pattern closely related to El Niño activity. Sea-level pressure (SLP) anomalies propagate eastward with the ACW. High SLP anomalies in the atmosphere correspond to low-density anomalies 111 the ocean. The ACC has clockwise geostrophic velocity anomalies over high-density anomaly regions with upwelling. Both heat and salt are transported from the deep layer to the surface layer by upwelling. This could suppress sea-ice formation directly. Anomalous horizontal advection of heat and salt by geostrophic velocity anomalies in the ACC appears to influence the anomalies in SST, SSS and sea ice.

The increased interest in past climatic changes, as revealed by studies of long ice cores from polar ice sheets, has stressed the need for a better understanding of the development of the stratigraphic record preserved in these cores. This paper presents some results of surface investigations at Dome C (74°30'S, 123°10'E), East Antarctica, carried out in austral summers 1978-79 and 1979-80. An explanation is presented of the snow stratigraphy, in terms of depositional and post-depositional processes, that is supported by detailed accumulation measurements at stakes and by snow-pit studies. Temporal and areal variability of snow accumulation are investigated to determine how representative the results interpreted from a single core might be for the Dome C region. Finally, the reliability of several stratigraphic methods for defining annual layers is assessed.

Snow-pit studies show that major depositional features are preserved with depth. Visible annual strata at Dome C are composed of thin, hard crusts overlying thicker layers of soft to medium-hard snow. Low density depth-hoar layers, when they occur, are usually found below the thin, hard crusts. Depth profiles of gross 8-radioactivity and of microparticles concentration exhibit annual cyclicity which, together with the detailed visible stratigraphy, can be used to assign dates to the layers.

A model using upper-air meteorological variables in the US National Centers for Environmental Prediction and US National Center for Atmospheric Research (NCEP/NCAR) re-analysis database is used to extend net balance bn back to 1948 for seven glaciers in southern Norway. The observational record of another glacier, Storbreen, began in 1948. Over the observational record of each of the seven glaciers, correlation with Storbreen estimates bn more accurately than the upper-air model does for four of them and less accurately for three. In all seven cases, however, an average of the model and the Storbreen correlation is more accurate than either alone, so the average is used to reconstruct bn for years when it was not observed. For the seven glaciers other than Storbreen, a combined series is formed from observations during their period of record and from reconstructed values prior to then back to 1948. There are three distinct sections in all eight bn series: prior to 1989; 1989–1995, when the North Atlantic Oscillation index was strongly positive; and after 1995. The 1989–95 mean bn was anomalously positive because of both decreased ablation and especially increased accumulation. The mean bn since 1995 has been anomalously negative because of increased ablation, whilst accumulation has been nearly the same as over 1948–88. The first principal component of the eight 1949–2005 bn series explains 78% of the total variance, and the second explains 12%. Over 1949–88 there were no substantial shifts in bn or in either winter balance bw or summer balance bs at any of the seven glaciers where observations began after 1948, nor were there in the Storbreen record. There is a distinction between the three glaciers that gained mass over 1948–2005 and the five that lost mass. Each of the three that gained had accumulation-area ratio AAR ≥ 0.64 and <0.7% of its area δS in the lowest tenth of its altitude range, while the five that lost had AAR ≤ 0.46 and 1.9 ≤ δS ≤ 4.4%. Because of these hypsometries, the five glaciers that lost mass now have an especially large ablation area.

A computer-based climate monitoring project is described. Data sets include monthly and annual mean surface temperatures and pressures for occupied stations in Antarctica, the Southern Ocean and South Pacific Ocean; and monthly Antarctic sea-ice extent at each 10° of longitude.

Simple statistical analyses of the data sets reveal a mean warming of ~0.15°C (10 a)−1 since the mid 1950s for Antarctic coastal stations and of ~0.04°C (10 a)−1 since the mid 1940s for the ocean stations. The sea-ice record from 1973 to 1988 reveals that the average northern ice limit has decreased at ~0.23°lat. (10 a)−1. Despite apparently compatible long-term trends of temperature and sea-ice extent, annual fluctuations of temperature and ice extent are highly variable and are not well correlated.

Active seismic imaging of glaciers and ice sheets is important for constraining inputs to climate models, such as englacial ice fabric and the nature of the basal interface. However, acquiring high-quality seismic data is time-consuming and resource-intensive. Using traditional single-element geophones requires ideal weather conditions (e.g. light winds) and excellent source coupling. In addition, deploying and retrieving these geophones is slow and cumbersome. We have developed a four-element ‘georod’ that enhances signal levels by 20–30dB in a variety of conditions, including blowing snow and poorly coupled source detonations. The long, slender design of these georods makes them easy to deploy and retrieve, allowing researchers to acquire greater line-kilometers of seismic data during field campaigns that are commonly time-constrained.

Hydraulic processes within and beneath glacial bodies exert a far-reaching control on ice flow through their influence on basal sliding. Within the subglacial system, rapid changes in these processes may excite resonances whose interpretation requires an understanding of the underlying wave mechanics. Here, we explore these mechanics using observations from a kHz-sampled pressure sensor installed in a borehole directly above the hard granite bedrock of a temperate mountain glacier in Switzerland. We apply a previously established theory of wave propagation along thin, water-filled structures such as water-filled voids, basal water layers, or hydraulic fractures. Within such structures, short-wavelength waves experience restoring forces due to compressibility and are composed of sound waves. Long-wavelength resonances, in contrast, experience restoring forces due to elasticity and are composed of anomalously dispersed crack waves or Krauklis waves. Our borehole observations confirm the occurrence of both sound and crack waves within the basal water layer. Using both the resonance frequencies and attenuation of recorded crack waves we estimate thickness, aperture and length of the resonating basal water layer patch into which we drilled. We demonstrate that high-frequency observations of subglacial hydraulic processes provide new insights into this evolving dynamic system.

Sulphate (SO42–) is a major ion found in polar ice cores and is related to different aerosol sources and processes. Explosive volcanic eruptions, even far away, can cause distinct sulphate peaks in ice core records. Thus, a robust sulphate detection system which is suitable for fieldwork and which enables the measurement of sulphate at high temporal resolution is of great interest. In this study, we present the adaptation of a new continuous flow analysis system for sulphate that is based on a spectrophotometric method using dimethylsulfonazo III and an inline reactor column containing barium sulphate particles. The method shows a detection limit of ∽70 ng g–1 and a linear range up to at least 3000 ng g–1. It is simple, robust and less prone to interferences compared to the previously used method.

To determine annual layers for reconstructing the past environment at annual resolution from ice cores, we employed snow-stake data back to 1972, tritium content, solid electrical conductivity measurements (ECM) and stratigraphic properties for the 73m ice core at the H72 site, east Dronning Maud Land, Antarctica. the average annual surface mass balance at H72 is 307 mma–1w.e. during the last 27 years from continuous accumulation data, 317 mma–1 w.e. according to the densification model and 311 mma–1 w.e. according to the average surface mass balance for 167 years based on annual-layer counting. the ECM age is closely coincident with tritium age, and corresponds with the snow-stake record back to AD 1972 from the surface to 15 m depth. the H72 ice core is dated as AD 1831by ECMat 73.16 mdepth.The time series of yearly surface mass balance at H72 shows an almost constant 311 mm a–1 w.e. for the last 167 years. the oxygen-isotope records indicate a significant trend to lower values, with negative gradient of 1.7% (100 years)–1.

A physically based numerical model of drifting and blowing snow in three-dimensional terrain is developed. The model includes snow transport by saltation and suspension. As an example, a numerical simulation for an Alpine ridge is presented and compared with field measurements.

Fabric analysis of the upper 1300 m of the Dome C (East Antarctica) ice core reveals a slight clustering tendency of c axes towards the vertical, which gradually enhances with depth from an initially isotropic orientational distribution of c axes at the free surface. Such a strain-induced anisotropy is compatible with the expected macroscale stress state in a dome, i.e. dominated by vertical compression. Yet, when one analyzes the orientational distribution of the visible gliding layers of individual crystallites (slip bands), the evidence is quite contrasting. Direct observation of slip bands in samples from the Dome C ice core taken from different depths (204–1291 m) indicates a higher slip activity in nearly horizontal planes, in such a manner that >60% of the detected slip bands have an inclination of <30˚ with respect to the horizontal. Furthermore, the observed slip activity is not symmetric, i.e. the number of slip bands discerned at 20˚, say, is usually not comparable with the number found at 160˚. Such features are not consistent with the predicted slip activity induced by compression and/or extension. In this work, we present evidence for this unexpected orientational distribution of slip bands and discuss some of the possible causes. Natural and artificial agents are investigated, together with their respective consequences for ice-sheet modeling and ice-core processing. Additionally, we show the occurrence of bent slip bands in certain crystallites. Such a bending represents an early stage of polygonization, and highlights the strong inhomogeneity of deformation at the crystal level. Moreover, it indicates that polygonization might be mathematically interpreted as a continuous process of rotation, characterized by the divergence of c axes from a common direction.

Fourteen subglacial debris samples have been recovered from the margins of, or beneath, Haut Glacier d’Arolla, Switzerland. The grain-size distributions of these sediments are presented and compared with each other as bivariate plots of percentage weight against (sieve-defined) particle size and log number of particles against log particle diameter. All of the samples recovered are composed of a broad range of clast sizes and approach self-similarity over the four orders of magnitude of grain-sizes analysed. Fractal dimensions range from 2.47 to 2.77. Sample intercomparison reveals the operation of at least two processes of textural evolution: the production of fines by in-situ weathering, interpreted in terms of abrasion associated with subglacial sediment deformation, and the loss of fines, interpreted in terms of eluviation by percolating subglacial meltwaters. These interpretations are supported and refined through comparison of the grain-size fractions gained (in the case of deformation) and lost (in the case of eluviation) with those fractions respectively generated in a laboratory-based simulation of sediment deformation and exiting the glacier suspended in the proglacial meltwater stream. While sediment deformation has the effect of increasing the fine fraction between 0 and 10ϕ and of raising the fractal dimension of undeformed sediments from 2.47 to 2.77, eluviation removes particles between 2 and 100, driving the fractal dimension of deformed sediments down from 2.77 to 2.54. These fractal dimensions are generally lower than those recorded at other comparable glaciers, consistent with the relatively low rates of sediment deformation inferred from other studies at Haut Glacier d’Arolla.

A highly polluted rain event deposited ammonium and nitrate on Midtre Lovénbreen, Svalbard, European High Arctic, during the melt season in June 1999. Quasi-daily sampling of glacial runoff showed elevated ion concentrations of both ammonium (NH4+) and nitrate (NO3−), collectively dissolved inorganic nitrogen (DIN) in the two supraglacial meltwater flows, but only elevated NO3− in the subglacial outburst. Time-series analysis and flow-chemistry modelling showed that supra- and subglacial assimilation of NH4+ were major impacts of this deposition event. Supraglacial assimilation likely occurred while the pollution-event DIN resided within a/the supraglacial slush layer (estimated DIN half-life 40–50 hours, with the lifetime of NO3− exceeding that of NH4+ by 30%). Potentially, such processes could affect preservation of DIN in melt-influenced ice cores. Subglacial routing of event DIN and its multi-day storage beneath the glacier also enabled significant assimilation of NH4+ to occur here (60% of input), which may have been either released as particulate N later during the melt season, or stored until the following year. Our results complement existing mass-balance approaches to the study of glacial biogeochemistry, show how modelling can enable time-resolved interpretation of process dynamics within the biologically active melt season, and highlight the importance of episodic polluted precipitation events as DIN inputs to Arctic glacial ecosystems.

Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study ice-flow dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the iceberg-calving front of the Filchnei—Ronne Ice Shelf, Antarctica. The interferograms are constructed from SAR images provided by the European Space Agency's remote-sensing satellites (ERS-1/2). Narrow bands of large shear strain rate are observed along the boundaries between fast-flowing ice-shelf ice and no-flow boundaries. Large rifts, opened where the ice shelf separates from the coast, appear to be filled with a melange of sea ice, ice-shelf fragments, and snow. Trial and error is used to find the best match between artificial interferograms, constructed from modelled ice flow, and the observed interferograms. We find that at both HIR and LC, ice with in the coastal boundary layers must be significantly softer than adjacent ice. At HIR the rift-filling ice melange transmits stress from one ice-shelf fragment to another; thus it must have mechanical competence and must moderate both separation of the ice shelf from the coast and the release of icebergs. However, the ice melange along the LC does not. The difference may be related to melange thickness, which could vary in the two locations due to differences in sub-ice-shelf oceanography or perhaps to regional atmospheric warming, currently under way along the Antarctic Peninsula. Future warming could weaken the melange ice around HIR as well, causing the ice shelf to lose contact with that shelf-front anchor.

Radio-wave scattering is a convenient method to image the properties of large internal regions of ice sheets. We used a ground-based radar system with short pulses of 60 and 179MHz frequencies to scatter off internal strata within 100–700 m of the surface in the ice sheet of East Antarctica. Data were examined along an 1150 kmlong traverse line that was approximately along the ice flowline from inland of Dome Fuji station to the coast. The scattered waves are from strata, and the dominant cause of the scattering was changes in dielectric permittivity across the strata. Therefore, density fluctuations primarily cause the scattering, although variations in ice-crystal fabrics and acidity could also have effects. The power scattered from the same depths varied by > 15 dB from one location to another. These variations correlate with the accumulation rate, changes in the surface slope, and subglacial bedrock undulations. Variations of the scattered power suggest that density contrasts in the strata are highly variable depending on these interdependent local conditions. The distribution of strata along the route allowed estimates of the ice-flow trajectories to depths of about 250 m.

A free-drift sea-ice model for advection is described which includes an interactive wind-driven ocean for closure. A reduced system of equations is solved economically by a simple iteration on the water stress. The performance of the model is examined through a sensitivity study considering ice thickness, Ekman-layer scaling, wind speed, and drag coefficients. A case study is also presented where the model is driven by measured winds and the resulting drift rate compared to measured ice-drift rate for a three-day period during March 1981 at about 80 km inside the boundary of the open pack ice in the Bering Sea.

The advective model is shown to be sensitive to certain assumptions. Increasing the scaling parameter A for the Ekman depth in the ocean model from 0.3 to 0.4 causes a 10 to 15% reduction in ice speed but only a slight decrease in rotation angle (α) with respect to the wind. Modeled α is strongly a function of ice thickness, while speed is not very sensitive to thickness. Ice speed is sensitive to assumptions about drag coefficients for the upper (CA) and lower (CW) surfaces of the ice. Specifying CA and the ratio of CA to CW are important to the calculations.

Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.

The surface velocity of Pine Island Glacier, West Antarctica, during the period 1992–2000 is measured with synthetic aperture radar feature-tracking techniques. Over the observation period, we find a monotonic acceleration with a spatially uniform amplitude of about 12% of the surface velocity. The acceleration extends > 80 km inland of the grounding line into a zone of prominent arcuate crevasses.The upper limit of these crevasses has migrated up-glacier by 0.2 km a−1 correlated with a velocity increase of similar size in the crevassed zone. On the other hand, there is no clear correlation between the velocity variations and observations of grounding-line migration. These findings suggest ongoing dynamic thinning of Pine Island Glacier, providing independent confirmation of recent interferometric results obtained by Rignot and others (2002).

A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.

It is generally accepted that fresh-water fluxes due to ice accretion or melting profoundly influence the formation of Antarctic bottom water (AABW). This is investigated by means of a global, three-dimensional ice–ocean model. Two model runs were conducted. At the high southern latitudes, the control experiment exhibits positive (i.e. towards the ocean) fresh-water fluxes over the deep ocean, and large negative fluxes over the Antarctic continental shelf, because of the intense ice-production taking place in this region. The salinity of shelf water can increase in such a way that deep-water formation is facilitated. The simulated net fresh-water flux over the shelf has an annual mean value of −1 m a−1. This flux induces a transport of salt to bottom waters, which corresponds to an increase of their salinity estimated to be around 0.05 psu. In the second model run, the fresh-water fluxes due to ice melting or freezing are neglected, leading to a rearrangement of the water masses. In particular, the AABW-formation rate decreases, which allows the influence of North Atlantic deep water (NADW) to increase. As NADW is warmer and saltier than AABW, the bottom-water salinity and temperature become higher.